1. Field of the Invention
This invention relates to an apparatus for controlling a throttle valve in a car engine in which the throttle valve in the engine is operated by an electronic control.
2. Description of the Prior Art
Recently, in order to improve the driving feeling and the roadability of a car, an apparatus for controlling a throttle valve has been developed in which an accelerator pedal is not connected with the throttle valve by means of the conventional simple mechanical means such as a wire cable, but instead an electronic device is disposed between the accelerator pedal and the throttle valve to open and close the throttle valve based on the driving condition of the engine and the traveling condition of the car in addition to the amount of the accelerator pedal depression.
This apparatus for controlling a throttle valve requires a number of driving information sensors including a sensor for detecting the amount of accelerator pedal depression, and also requires an actuator for operating the throttle valve and an electronic control device for treating signals from the respective sensors and controlling the actuator. It thus becomes complicated in comparison with the conventional control using only a wire cable. As a result, reliability problem occur.
Further, a fail-safe mechanism is required to prevent the car from running away due to a malfunction in the electronic control device, and to prevent the throttle valve from being suddenly closed to brake the car during high-speed travel.
In the fail-safe mechanism of a conventional electronic control device of this type, a return spring for returning the throttle valve to a closed position when a malfunction has occurred is mounted on the throttle shaft. However, this conventional fail-safe mechanism has shown problems in that when the actuator fails the car can be prevented from running away, but the travel of the car cannot be maintained. Thus the car cannot be driven to a repair facility, and thee is the possibility that the car will be suddenly braked and bumped from behind during its high-speed travel.